A plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas. Plasma behavior may be extraordinarily varied and subtle. In particular, hydrodynamic motion in imploding plasmas is not well diagnosed at all relevant spatial scales. It has been theorized that bulk macroscopic motion can be imparted to regions of imploding plasmas by three-dimensional effects, serving as a sink for energy that would otherwise go towards heating the plasma. However, there has been no ability to directly diagnose such motion.
It is known that astronomers utilize Doppler shifted electromagnetic radiation emission as a diagnostic of material motion in space. This is typically a direct time-domain frequency measurement in the radio region of the spectrum, and measures line-of-sight velocities in objects such as nebulae and galaxies Likewise, Doppler shift analysis of sound and light waves is known.